Unbalanced to balanced broadband impedance transformer



A ril 5, 1966 w. BUSCHBECK UNBALANCED TO BALANCED BROADBAND IMPEDANCETRANSFORMER 4 Sheets-Sheet 1 Filed March 21, 1962 INVENTOR Werner Buschbeck ATTORNEY April 1966 4 w. BUSCHBECK 3,245,009

UNBALANCED TO BALANCED BROADBAND IMPEDANCE TRANSFORMER Filed March 21,1962 4 Sheets-Sheet 2 INVENTOR Werner Bu sch beck BY zgqgqafzww/ATTORNEY A ril 5, 1966 w. BUSCHBECK 3,245,009

UNBALANGED TO BALANCED BROADBAND IMPEDANCE TRANSFORMER Filed March 21,1962 4 Sheets-Sheet .5

Fig. 5a

INVENTOR Werner Buschbeck ATTORNEY A ril 5, 1966 w. BUSCHBECK 3,245,009

UNBALANCED TO BALANCED BROADBAND IMPEDANCE TRANSFORMER Filed March 21,1962 4 Sheets-Sheet 4 R k m w n b w h M m w 0 u T B m k. M '4 n w 1 N Nm W h I ew t N llllflll m m m Y I w MEN p a Q N\- N United States PatentT 16 Claims. (ct. 333-26) The present invention relates generally to thehigh frequency art, and, more particularly, to a device for connecting acoxial line with a balanced line having a higher characteristicimpedance and for eliminating the pulse which would otherwise occur.Such devices are known as balancing-transformer devices or matchingbalun devices.

The known balancing loop may he used for rebalancing, i.e., in thetransition from a coaxial unbalanced line to a balanced line, without asimultaneous transformation to another impedance. Furthermore, it istaught in GermanPatent No. 743,669 that the symmetric or balancedterminals of such a balancing loop may be connected by means ofcompensating members, with the low resistance balancing terminals of atransformer loop acting as an ideal transformer having a transformerresistance ratio of 1:4. This transformation is provided by a specialarrangement of the transformer loop wherein two halves of the outerconductor are connected in parallel and they thus provide a resultingcharacteristic impedance Z. The two halves of the inner conductor areconnected in series providing a resulting characteristic impedance of 4Zand thus four times the value of Z. It was thus possible to change orhave a transition from a coaxial unbalanced line having thecharacteristic impedance Z to a balanced line having the characteristicimpedance 4Z by using the device taught in the afore-mentioned Germanpatent.

However, a device which produces transformer ratios of 1:4 betweencoaxial and balanced lines in a simple manner frequently does notsatisfy practical requirements. For example, it is frequently necessaryto have a transition from the standard coaxial line resistance of 60ohms to a resistance of 340 ohms for a balanced four-wire line, or thestill higher resistance of 500 ohms for a balanced twowire line. Inthese cases the transformer ratio is as high as 1:5.5 through 1:7.5.

German Patent No. 806,446 teaches a device for the transition from ahigh frequency unbalanced device, i.e., one which is asymmetrical withrespect to ground, to a high frequency balanced device, i.e., one whichis symmetrical relative to ground, with simultaneous resistance matchingor transformation wherein ratios are provided which are difierent fromthe value of 1:4. This device has an unbalanced line divided into anumber of branches which, when viewed from the branching point, areconnected in parallel and with the free ends of the branches connectedin series. In this device means are used to prevent voltage equalizationbetween the free ends via the outer covering of the lines. However, inusing this device, only transformer ratios having a value of lzX, whereX is the square of an integral number, may be produced.

In order to solve the problem it is also known to use a balancing loopor coil in connection with a quarter wavelength transformer or astaggering of such transformers in the form of a stepped line or anexponential line (German Patents No. 845,967 and No. 955,065)

However, with these devices, resistance ratios of from 1:5 through 1:8can be matched only by having a great number of steps in the steppedline or with an exponential line of a considerable length, if the deviceis to be used for a frequency band having a substantial band width.Therefore, these devices generally require an undesirably large amountof equipment and are accordingly expensive to produce and occupy a greatdeal of space.

In all of the balancing-transformer devices mentioned above, it isfundamentally necessary to provide additional compensating members ifthe device is to operate within a large frequency range withoutundesired or inadmissible changes of the transformer ratio. The designof such compensating members is basically known and several of thesemembers may be provided at each end of the device. It is also known toenclose several coaxial line portions each into one another to providefor their structural housing (German Patent No. 944,615), or, forexample, the otherwise free leg of the balancing loop may be used forhousing a coaxial line portion of suitable characteristic impedancewhich is open at one end and is a quarter wave in length. Further, it isalso known to use the balancing loop itself as a compensating member byproviding it with a suitable characteristic impedance (German Patent No.738,664).

With these defects of the prior art in mind, it is a main object of thisinvention to provide a balancing-transformer device which may be used ina range of transformer ratios of 1:4 through 1:10 and which possessesgood performance and simplicity of design.

Another object of this invention is to provide a device of the characterdescribed which reduces the amount of 7 space required for the device.

.A further object of the present invention is to adapt such a device tohave its members for multiple compensation housed within the loop devicewithout requiring substantially more circuitry and without involvingfurther expense.

Still another object of this invention is to provide a device of thetype described which is extremely compact and is disposed in itsentirety within a common housing.

These objects and others ancillary thereto are accomplished according topreferred embodiments of the invention wherein a device is developedfrom a known combination (German Patent No. 743,669, particularly FIG-URE 3) of the balancing loop with a 1:4 transformer loop. It is possibleto construct the device so that the transformer ratio Within thementioned limits may deviate from the value 1:4. A combination of a onestage or multiple stage quarter wavelength transformer will suit thispurpose very Well. The invention uses a device for the transition from acoaxial line to a balanced line of higher characteristic impedance.

This device has a balancing loop and a transformer loop, with thetransformer loop connected to connection points of the balancing loop bymeans of compensating elements for a resistance or impedance ratio of1:4. The device is preferably provided with an open quarter wavelengthline housed in the interior of the otherwise free leg of the balancingloop, and serves as compensating element. Preferably, it is alsoprovided with an open quarter Wavelength line housed in the interior oftubular initial portions of the conductors of the balanced line andserving as compensating member.

According to the present invention, the balancing loop and thetransformer loop are substantially equal in size and closely adjacenteach other. They are disposed in a mirror image position relative to aplane of symmetry which is parallel to the planes of the loops, asdetermined by the line axes of the loop portions belonging in the sameloop plane. However, in each case, one leg is coordinated with thebalancing loop, andthe other leg is coordinated with the transformerloop. Also, outlets which are dis pose-d on the side ofthe coaxialconnection of the balancingv loopfor the initial portions of theconductors of the balancing line are defined by apertures in the outerconductors. These apertures also have a: mirror image posi-' tionrelative to the plane of symmetry mentioned above, and are disposed inthe electrical center of the loops. Moreover, the twoinitial portionsare disposed remote from these outlets at right angles tothe plane ofsymmetry, and are bent in a direction parallel-to the plane of;symmetry, at a distance which results in the desired characteristicimpedance. They are led to connections to the balanced line andtheinitial portions mentioned have a mirror image position relative tothe plane of symmetry and its axes, and is disposed within theequipotential plane of the loops.

By combining the two loops which act as an ideal transformer of thetransformer ratio l :4, the characteristic impedances of thecompensating members on the input side are reduced to one-fourth of theotherwise necessary value, and thereby obtain practical, usable valueswithlittle expenditures.

It must be noted that the pointof the transformation begins directly atthe open end ofv the balancing loop where the inputs of the two sidesofQthe transformer loop are fed. However, while, as stated above, thequarter wavelength compensation line which is open at the input side,can easily be accommodated in the leg of the balancing. loop which isreadily accessible at that point and is otherwise free, the 1:4impedance transforrnation occurs only at the short-circuitedend; of theloop where the two outer conductors-whose inputsides are fed in phaseoppositioncan be connected together with inverse polarity so that theoutput voltage is, independently of its relative phase position withrespect to the. input voltage, just exactly doubled with respect. to thevaiue applied through a single line.

. This combination. of the loopsprovidesa reduction in the volumerequired as compared totheknown devices according to German Patent No.743,669. There is a special coordination of the individual legs of theloop according to which the spatially correlated loops disposed on both.sides of the plane of symmetry mentioned above, each receives one leg.of the balancing loop and one leg of the transformer loop. This providesthe possibility of designing the initial portions which leave or exitfrom the mentioned apertures of the outer conductor loop and which areinitial portions of the balanced line, in a maner which. allows them tobe likewise spatially exactly symmetrical relative to the plane ofsymmetry mentioned above and. allows themto be led into the.equip'otential plane of the loop device and thus in the electricallyneutral plane. This is particularly important in view of the necessarydecoupling of the balanced line from the field of the loop device. Thus,the present, invention provides the feature that the total constructionis extremely com pact and all of the parts may be housed within acornmonhousing.

Additional objects and advantages of the instant invention will becomeapparent upon consideration of the following description when takeninconjunction with the accompanying drawings in which: 7

FIGURE 1 is a perspective view of the baianc-ingdransformer device withthe housing thereof broken away for clarity.

FIGURE 2 is a schematic circuit diagram illustrating the equivalentcircuit of the device of FIGURE 1.

FIGURE 3a is a schematic elevational side view of another embodimentsimilar to that of FIGURE 1.

FIGURE 3b is a front elevational view of the device illustrated inFIGURE 3a having a rectangular housing.

FIGURE 3c is a front elevational view similar to that of FIGURE 31) butshowing a cylindrical housing.

FIGURE 4 is a schematic circuit diagram of the equivalent circuit of thedevice of FIGURES 3.

FIGURE 5a is a schematic elevational side view of another embodiment ofthe invention illustrating a two stage arrangement.

FIGURE 51) lliustrates a front elevational view of the embodiment ofFIGURE 5a.

FIGURE 6 is a schematic view illustrating. a device constructed inaccordance with the present invention.

FIGURE 7 is a circuit diagram-illustrating the equivalent circuit ofFIGURE 6.

With more particular reference to the drawings, FIG- URE 1 illustrates afirst embodiment of a balancing-transformer device designed in'accordance with the present invention.- Terminals or connections 1 and 2of the balanced line proper are provide/don one side ofhousing 4, whileaconnection or terminal 3 for the coaxial line disposed on the otherside thereof. The. characteristic impedanceof coaxialline terminal 3have a value Z and is equal to the matching resistance R This matchingresistance value may correspond to one which occurs in actual practiceand may be, for example, 60 ohms.

In FIGURE 1, two loops are shown disposed one above the other with theouter conductors 5 and 6 for the balancing loop and the outer conductors7 and 8 for the transformer loop. The inner conductors of the transformer loop are connected with the outer conductorsof the opposite legsby means of the connecting bridges and Iii. The connecting bridge 11.forms a connection between the inner conductor of the balancingloop andthe outer conductor of the opposite leg of this loop. However, acompensating element or line which is a quarter wave in length isinserted, is open at it'send, has a characteristic impedance Z andisd'ispose'd' within the interior of outer conductor 6.

This device will be even clearer if the current path is traced fromthecoaxial line connection or terminal 3 to the connections 1 and 2 for thebalanced line proper. Beginning with the connection 3, the innerconductor thereof. firs-t turns into the leg which is disposed at thelower right and is a leg ofthe balancing' loop, the outer conductor ofwhich is designated 5'. This log of the balancing lo'op ha'sjthecharacteristic impedance Z and is thus equal to the characteristicimpedance of the coaxial line terminal 3. At the separation point ofthis loop device, the connection continues, via the connecting member11, from the inner conductor to the compensating line which has thecharacteristic impedance Z By the insertion of this compensating linesection, the con-' nection of the inner conductor to the outer conductorof the opposite leg, which is required anyway, is thus established.

The two ends of the outer conductor at the separating point now form theconnection points of the balancing loop. The high frequency currentarrives, via the connecti'ons 9 and 10, at the inner conductors of thelegs of the transformer loop from these. balanced connection points andthus at the leg which is located at the upper right and the leg in thelower left of the drawing. These logs are designed to have thecharacteristic impedance 2 /2, the importance of which will be discussedbelow inconnection with the equivalent circuit.

The inner conductors of the transformer loop are bent at 1'2 and 13 andthey pass from the interior tothe exteriorof the outer conductorsthrough corresponding apertures and are disposed perpendicular to thecentral plane of the loop device. These-conductors immediately entertubular outer conductors 16 and 17 and form the inner conductors 14 and15 thereof. The outer conductors form the beginning or initial portionsof the balanced line which is symmetrical with respect to ground. Theyare chosen to be of such thickness that the beginning portions whichthey form are provided with the desired characteristic impedance Z Innerconductors 14 and 15 and the associated outer conductors 16 and 17 formportions which are a quarter wave in length and are open at the end andact as compensating members having a characteristic impedance of 2 2.

These inner conductors 14 and 15 end at the points 14, 15'. In order toimprove the spatial symmetry of the device which is disturbed somewhatdue to the eccen tric position of the coaxial line for terminal 3, adummy socket 18 is provided. This dummy socket has no other electricalfunction to fulfill except as mentioned above.

From FIGURE 1, it may be seen that the initial portions 16 and 17 of thebalanced line, which are parallel to the symmetrical plane, spatially,enclose two loops between them. The terminals of the balanced line aredisposed on the side of the device which is opposite to that of thecoaxial terminal 3. Thus, all par-ts of the device are housed relativelyclose to each other without mutually disturbing one another in anelectrical sense. The entire device requires little volume and hasexcellent mechanical and electrical properties. This device may beplaced in positions where it is subject to the elements without anyprotective casing, if the openings in the outer conductors areprotected, in a manner which is known per se, to prevent penetration bymoisture.

FIGURE 2 illustrates an equivalent circuit wherein the coaxial lineportions are indicated as Lecher wires in order to clarify the drawing.Tracing the path of the high frequency energy from terminal 3 to theterminals 1 and 2 will more clearly demonstrate the effect of thecompensating members and the transforming elements.

It will be assumed that the characteristic impedance of the terminal 3 Zis equal to 60 ohms and that it corresponds to the value. of thematching resistance R ;The transformation in the 1:4 ratio takes placeat the separating phantom l-ine A'B. Therefore, it may be imagined thatan ideal transformer is disposed at this point having a resistancetransformer ratio of 1:4. The compensating elements on the input sideare formed by the line section which is open at the end and has thelength l and the characteristic impedance 2.; and includes outerconductor 6 and inner conductor 6'. Also comprising the compensatingelement is the line section which is short-circuited at the end and hasthe length l and a characteristic impedance Z and these elements aredisposed on the low resistance side of the transformer.

The short-circuited line section is formed by the outer conductors 5 and7 of the double loop which are disposed one upon the other as well asthe outer conductors 6 and 8 0n the other side. The transmission lineshaving the characteristic impedance 2 /2 and formed by the two legs ofthe transformer loop are connected on the high resistance side of thetransformation point A-B. These line sections also have a length l whichis approximately equal to kHz/4, and thus to a quarter wavelength withrespect to a mean frequency of the range to be covered. The outerconductors 7 and 8 of these transmission line sections are housed in thelegs of the trans former loop.

In order to provide a matching of a value which deviates from thefourfold of the impedance match on the unbalanced side and preferably toa higher value in the case of an embodiment according to FIGURES 1 and2, the two legs of the transformer loop are designed as a N4 transformerhaving the characteristic impedance 2 /2. Z at least substantiallycorresponds to the geometric mean between the fourfold value mentionedabove and the desired deviating value. In FIGURE 2, it is assumed thatthe transformation is to be carried out for a resistance R of 340 ohmson the balanced side which corresponds to the characteristic impedanceof a conventional four-wire line.

Uunder these assumed conditions, a value of 260 ohms is provided for Zso that Z /2 is ohms. The design of these line portions in legs 7 and 8of the transformer loop having the characteristic impedance 2 /2 may befound when it is considered that, as seen from the balanced side, thecharacteristic impedances of these two line portions appear to beconnected in series.

In FIGURE 1, a balanced line is shown which has a characteristicimpedance Z which is equal to 340 ohms and which is connected at thepoints 12 and 13. Using distances between the two conductors which arestill technologically feasible, this characteristic impedance results inthe conductors being relatively large in diameter. Therefore, theinitial portions 16 and 17 of the balanced lines are of tubular form andcontain inner conductors 14 and 15 interiorly thereof. Together, theinner conductors and outer conductors form compensating members whichare open at the end, have the characteristic impedance 2 /2, and are ofa length l.

The characteristic impedances of the compensationg members Z Z.,, and Zmay be determined according to known formulas and therefore there is noneed for a further discussion thereof. However, it should be noted thatwhen considered from the balanced side of the characteristic impedance 2/2 of the intial portions 16 and 17 appears to be connected in series,and this explains the value of being Z /2. As shown in FIGURES 1 and 2,the invention provides not only an exceedingly simple and space-savingbalancing and transforming device, but also provides a transformer ratiowhich deviates from the value 1:4 without any additional expense.

With reference now to FIGURES 3a and 3b, a device is illustrated whichis similar to FIGURE 1 with different diameters of the conductors of thecoaxial line sections being indicated. If the housing 4, which coversthe device, is of a conductive material, then there are certainconditions which must be met as to its spacing from the outer conductorsin order to assure that the desired characteristic impedances areprovided. These characteristic impedances are: (l) Z of the intialportions of the balanced line; and (2) Z of the loop section. In orderto determine the proper design and dimensions for the housing, knowncalculations are required, such as those which are taught inTelefunken-Zeitung, March, 1961, Issue 131: Der Wellenwiderstandzylindrischer Leiter gegen verschiedenartig angeordnete ebeneSchirmwande (The Characteristic Impedance of Cylindrical ConductorsAgainst Differently Arranged Plane Screens), by W. Buschbeck. Thehousing 4 is shown in FIGURE 3b as having a square cross section withthe plane of symmetry of the loops forming a diagonal thereof, but thismay be replaced by an electrically equivalent housing 4' which is ofcylindrical form, as shown in FIGURE 3c.

The embodiments of FIGURES 3 are somewhat different from that of FIGURE1 in the compensating section of the initial portions 16 and 17 of thebalanced line. The inner conductors of the transformer loop pass throughoutlets or apertures in the outer conductors of the transformer loop andpass through the thicker outer conductors 16 and 17 and into the intialportions of the balanced line. These outer conductors now terminatewhile open at the point where in FIGURE 1 they directly change over tothe connecting conductors or terminals 1 and 2. Thus, the terminalpoints 14' and 15 of the inner conductors 14 and 15 of the compensatingmembers are now disposed near the exit points of the inner conductors ofthe transformer loop.

Due to this interchange of the terminals of the compensating members 14,16, and 15, 17, between the conductors 1 and 2, which are symmetricalwith respect to ground and the inner conductors leaving the transformerloop, the switch-in points of these line sections having the circuit of"FIGURE 2.

characteristic impedance Z 2 are shifted to the terminal points of thebalanced line conductors 1 and 2 as shall be discussed below inconnection with FIGURE 4. This displacement of the compensatingmembersdirectly to the output ofthe device advantageously provides'thepossibilityof designing the intialportion, formed by the outerconductors 1'6, 17, of the line symmetric to ground as a quarter.wavelengthtransformer stage, and of designing the correspondingcharacteristic impedance accordns yl The impedance matchontheasymmetrical side may be transformed'to a value which deviates fromthe fourfold value and preferably to a" higher value. This may beachievedbecause the two initial portions 16 and 17 of the balancedconductors are arranged as a'quarter wavelength transformer having thecharacteristic impedance Z The impedance Z at least substantiallycoresponds to the geometrical mean .between the matching impedanceprevailing at the connections of the, initial portions mentioned to theinner conductors of the transformer loop and the desired deviationvalue.

This feature will now be discussed with reference to the equivalentcircuit of FIGUREA. jltiwill be assumed, for purposes of explanation,that the transformation is to be effected from a coaxial inputresistance R, of

a balanced output resistance R, of 500 ohms." The-intial portion of thiscircuit .of .FIGURE 4 is identical with that of FIGURE 2 up to the rightside of the legs of the transformer loop having the characteristicimpedance Z /2.

The .twoportions having the characteristic impedance Z /2 form a firststage'of a quarter wavelength-transformer. An outputresistance or 340ohms could be connected .to, their ends without a voltage surge, in theIn the circuit or FIGURE 4, large to connect the output resistance of500 ohms, and it would no longer be possible to obtain favorable wideband characteristics. Therefore, the "second quarter wavelengthtransformer stage having acharacteristic impedance Z is provided by 'theinitial portions of the balanced line; Under these conditions, 2 /2 hasa value of 146.5 ohms, while Z is 424 ohms. As mentioned above, theconnection points for the compensating open quarter wavelength linemembers 14, 1 6, and 15, 17, have characteristic impedances Z 2 and arenow dis-posed between the'end' of the line section having thecharacteristic impedance Z and the 500 ohm terminal.

' FIGURES 5 illustrate the spatial arrangement of a balancing-matchingdevice with a two stage quarter wavelength transformer which follows thetransformer loop. Par-ts which correspond to thosev of FIGURE 1 .are provided with the same reference numerals and a detailed description ofthese portions will be omitted. The initial portions of the balancedline are considerably thinner in design in accordance with the increaseof the characteristic impedance Z Calculations have proven that in spiteof this the compensating lines which are open at the output side andhave the characteristic impedance Z /2' may still be disposed withinthese conductor-s. Thus, the expensefor providing a device having anadditional twofold quarterwavelength transformationis not greater thanin a device having a one stage quarter wavelength transthe, transformerstage would be too formation." The characteristic impedances of theconsecutive line sections in the multistage t ransf-o rmer at leastsubstantially form, a geometric series in. a known manne EIGURE 6illustrates an embodiment for matching a 60 o m nbalance n to a 60mmalan e l i as the type of device which is needed for high powertransmitters where two wire Lecher lines cannot be used, but where fourwire Lecher lines must be used because of the magnitude of the power tobe transmitted. FIG- URE '7 illustrates the equivalent electricalcircuit of the device according to FIGURE 6.

60 ohms to In FIGUREo, parts which are similar to those of precedingfigures are given corresponding reference numerals. A terminal 3 isprovided for the unbalanced line and has an input resistance R of 60ohms on the left side and connected to this is the balancing loop,theitransformer loop, which is on the right side next to the balancingloop, and the compensating members on the output side which areconnected to terminals 1 and 2 on the balanced line and which provide anoutput resistance R of 360 ohms. It should be understood that theseloops are folded or coiled one on the other similar-to the devices ofFIGURES 1 and 3.

If the mentioned ratio of input to output resistance is used, thetransformer ratio which is provided, if a loop having a transformingratio 1:4 is used, is so small that by using a fourfold compensateddouble quarter wavelength transformation, a very large wave range ofabout 1:20 may be included. Calculation indicates that with an inputresistance of 60 ohms the characteristic impedance Z' --providingcompensation-of the combined loop is still somewhat too large to providea device which is in a practically useful form. However, by lowering theinput resistance a little to 54 ohms, a usable design can be provided.Therefore, this step has been used in the embodiment of FIGURE 6 and the"60 ohms is first lowered to a usable resistance by a transformer. Thisis provided by using the first'leg of the balancing loop which isdirectly connected with the input terminal 3. This leg is used as aquarter Wavelength transformer section and is designed t-ohave acharacteristic impedance Z which is smaller than the input resistance Rto be connected with the terminal.

In the embodiment of FIGURE 6, specific characteristic impedances of apractical embodiment are indicated. However, it should h e realized thatthe present invention is by no means restricted to this particularexample. The characteristic impedance Z of the above-mentioned leg ofthe balancing loop has a value of 57.1' ohms. Due to this reduction ofthe characteristic impedance, even in the compensating members, it ispossible to use the loop device itself as a compensating member with thecharacteristicimpedance Z' as has been discussed above. The equivalentcircuit illustrated in FIGURE 7' shows the connection' of the line onthe low resistance side of the device which line is formed by the loop,short-circuited at the end, and has a characteristic impedance Z';,.

' When a great deal of power is involved, there are difficulties inhousing the compensating quarter wavelength line sections, which areopen at the 'end and have the characteristic impedance Z'.; in thebalancing loop because by using such. a small characteristic impedancethe dielectric strength is no longer sufficient. Accordingly, in FIGURE6 the open quarter wavelength compensating line in the otherwise freeleg of the balancing loop is replacedv by two line portions which areconnected in parallel. The inner conductor of one line is disposed in atubular'inner conductor of the other line. The characteristic impedanceof the one line portion is Z.;,, and that of theot-her line portion isZ' From these lines, and due to the parallel connection, the resultingcharacteristic impedance is Z.;.

The remainder of this embodiment is similar to the embodiment of FIGURES3. However, on the output side asecond compensating element is providedin the form of a coil 2%) which has a central tap connected to-ground.This arrangement has the desirable effect of removing to ground staticcharges on the four-wire line connected to terminals 1 and 2. Thecharacteristic impedance Z; of the compensating element formed by thecoil is so large that itrcanbe provided only in the form of a coilwinding.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes, andadaptations, and the same are intended'to-be comprehended within themeaning and range of equivalents of the appended claims.

What is claimed is:

1. A device for connecting a coaxial line having a low characteristicimpedance to a balanced line having a higher characteristic impedance,said device comprising, in combination:

(a) a balancing loop having a hollow outer conduc- (b) a transformerloop; producinga 1:4 transformation ratio having a hollow outerconductor;

(c) at least one compensating section connecting said loops thereby toforma loop assembly;

((1) means for connecting a coaxial line with one electrical end of saidloop assembly; and

(e) means for connecting a balanced line with the other electrical endof said loop assembly and including initial portions of a balanced lineand a connection assembly including terminal portions for connectingsaid initial portions with a balanced line proper; and

wherein said device is arranged with (1) said balancing and transformerloops being of substantially the same size and arranged closely togetherin mirror image relationship with respect to a plane of symmetryparallel to the loop planes as determined by the loop axes through thesections of the loops,

(2) one leg of a loop in a plane being a portion of the balancing loopand the other leg of such loop being a portion of the transformer loop,

(3) the end of said loop assembly disposed adjacent the coaxial lineconnecting means having outlets formed therein for passage therethroughof said initial portions which are connected to said loop assembly, saidoutlets being defined by openings in said outer conductors and which aredisposed in mirror image relationship with respect to said plane ofsymmetry,

(4) said initial portions of said outlet projecting away from each otherat right angles to said plane of symmetry, said initial portions beingbent parallel to said plane of symmetry at a distance which produces thedesired characteristic impedance and leading to the balanced lineconnection assembly, and

(5) said initial portions being disposed in mirror image relationshipwith respect to said plane of symmetry with the axes there- Of disposedwithin the equipotential plane of said loops.

2. A device as defined in claim 1 wherein said cornpensating sectionincludes a quarter wavelength open line disposed interiorly of theotherwise free leg of the balancing loop.

3. A device as defined in claim 1 wherein said initial portions aretubular, and further comprising compensating members connecting saidloop assembly with said connection assembly and including a quarterwavelength open line disposed interiorly of each tubular initialportion.

4. A device as defined in claim 1 wherein said initial portionsspatially enclose said loop assembly between them, and said connectionassembly is disposed on the opposite end of said device from saidcoaxial line con= necting means.

5. A device as defined in claim 1 wherein the two legs of said tran frmer loop a e a q arter Wav eng h tr sformer having the characteristicimpedance 2 /2 for transforming to a val e d vi ting from he eurf lmatching impedance on the coaxial or unbalaneed side and preferably to ahigher value, and wherein Z at least substantially corresponds to thegeometric mean between this fourfold value and the desired deviatingvalue.

6. A device asdefined in claim 1 wherein said initial portions are aquarter wavelength transformer having a characteristic impedance atleast substantially corresponding to the geometric mean betweenthematching impedance at the point where the initial portions areconnected to the loop assembly and a desired valuedeviating from thefourfold matching impedance on the coaxial or unbalanced side; andpreferably to; a higher value.

7. A device as, defined in claim 1: wherein the legs of the loops are aqua er wave inlen'gt-h and the two consecutive outer conductors of theloops have such a characteristic impedance (Z that they form acompensating element in the form of a short-circuited quarter wavelengthline.

8. A device as defined in claim 1 comprising a housing enclosing all ofsaid loop assembly and said initial portions.

9. A device as defined in claim 8 wherein said housing is formed of anelectrically conductive material.

10. A device as defined in claim 8 wherein said housing is formed of aninsulating material.

11. A device as defined in claim 1 comprising a second compensatingelement connected between said terminal portions, said secondcompensating element being a coil having a grounded central tap.

12. A device as defined in claim 1 wherein a balancing loop leg isconnected to said coaxial line connecting means and is a quarterwavelength transformation line having a characteristic impedance whichis smaller than the input resistance to be connected to said coaxialline connecting means.

13. A device as defined in claim 2 wherein the open quarter wavelengthcompensating section is formed of two line sections connected inparallel with an inner conductor of one line section disposed in ahollow inner conductor of the other line section.

14. In a device for connecting a coaxial line having a lowcharacteristic impedance to a balanced line having a highercharacteristic impedance, and including a balancing loop having a hollowouter conductor, a transformer loop producing a 1:4 transformationratio, at least one compensating member connecting said loops to form aloop assembly, means for connecting a coaxial line with one electricalend of said loop assembly, and means for connecting a balanced line withthe other electrical end of said loop assembly and including initialportions of a balanced line and a connection assembly for connectingsaid initial portions with a balanced line proper, the improvement thatsaid balancing and transformer loops are of substantially the same sizeand arranged closely together in mirror image relationship with respectto a plane of symmetry parallel to the loop planes as determined by theloop axes through the sections of the loops, one leg of a loop in aplane is a portion of the balancing loop and the other leg of such loopis a portion of the transformer loop, the end of said balancing loopdisposed adjacent the coaxial line connecting means has outlets formedtherein for passage therethrough of said initial portions, said outletsare defined by openings in the outer conductor and which are disposed inmirror image relationship with respect to said plane of symmetry, saidinitial portions of said outlet project away from each other at rightangles to said plane of symmetry, said initial portions are ben parallelto said plane of symmetry at a distance which produces the desired characteristic impedance and lead to the balanced line connection assembly,and said initial portions are disposed in mirror image relationship withrespect to said plane of symmetry with the axes thereof disposed withinthe equipotential plane of said loops. I

15. A device as defined in clairn 1 wherein said transformer loop isformed of two coaxial conductors which are of substantially the samelength and the ends of whose corresponding outer conductors areconnected,

on the low ohmic side of the loop, with the ground References Cited bythe Examiner symmetry terminal points of the balancing loop, and, N ESTATES PATENTS on the high ohmic side of the loop, with each other, athe ends of the inner conductors are connected, on the 2998376 10/1939Zm.ke et 333 26 low ohmic side over a cross with the ends of the outer 52925566 2/1960 2 3326 conductors and, on the high, ohmic side, with thecon- 3066266 171/1962 Flsher 33325 nections of a conductor that issymmetrical. with respect OTHER REFERENCES to ground- Triolo et al.:Electronic Design, 'April 15, 1959, pages 16. A devlce as defined inclaim 1 wherein said b-alanc- 3 ing and transformer loops are arrangedin contact with 10 each other in mirror image relationship. HERMAN KARLSAALBACH, Primary Examiner.

1. A DEVICE FOR CONNECTING A COAXIAL LINE HAVING A LOW CHARACTERISTICIMPEDENCE TO A BALANCED LINE HAVING A HIGHER CHARACTERISTIC IMPEDENCE,SAID DEVICE COMPRISING, IN COMBINATION: (A) A BALANCING LOOP HAVING AHOLLOW OUTER CONDUCTOR; (B) A TRANSFORMER LOOP PRODUCING A 1:4TRANSFORMATION RATIO HAVING A HOLLOW OUTER CONDUCTOR; (C) AT LEAST ONECOMPENSATING SECTION CONNECTION SAID LOOPS THEREBY TO FORM A LOOPASSEMBLY; (D) MEANS FOR CONNECTING A COAXIAL LINE WITH ONE ELECTRICALEND OF SAID LOOP ASSEMBLY; AND (E) MEANS FOR CONNECTING A BALANCED LINEWITH THE OTHER ELECTRICAL END OF SAID LOOP ASSEMBLY AND INCLUDINGINITIAL PORTIONS OF A BALANCED LINE AND A CONNECTION ASSEMBLY INCLUDINGTERMINAL PORTIONS FOR CONNECTING SAID INITIAL PORTIONS WITH A BALANCEDLINE PROPER; AND WHEREIN SAID DEVICE IS ARRANGED WITH (1) SAID BALANCINGAND TRANSFORMER LOOPS BEING OF SUBSTANTIALLY THE SAME SIZE AND ARRANGEDCLOSELY TOGETHER IN A MIRROR IMAGE RELATIONSHIP WITH RESPECT TO A PLANEOF SYMMETRY PARALLEL TO THE LOOP PLANES AS DETERMINED BY THE LOOP AXESTHROUGH THE SECTIONS OF THE LOOPS, (2) ONE LEG OF A LOOP IN A PLANEBEING A PORTION OF THE BALANCING LOOP AND THE OTHER LEG OF SUCH LOOPBEING A PORTION OF THE TRANSFORMER LOOP, (3) THE END OF SAID LOOPASSEMBLY DISPOSED ADJACENT THE COAXIAL LINE CONNECTING MEANS HAVINGOUTLETS FORMED THEREIN FOR PASSAGE THERETHROUGH OF SAID INITIAL PORTIONSWHICH ARE CONNECTED TO SAID LOOP ASSEMBLY, SAID OUTLETS BEING DEFINED BYOPENINGS IN SAID OUTER CONDUCTORS AND WHICH ARE DISPOSED IN MIRROR IMAGERELATIONSHIP WITH RESPECT TO SAID PLANE OF SYMMETRY, (4) SAID INITIALPORTIONS OF SAID OUTLET PROJECTING AWAY FROM EACH OTHER AT RIGHT ANGLESTO SAID PLANE OF SYMMETRY, SAID INITIAL PORTIONS BEING BENT PARALLEL TOSAID PLANE OF SYMMETRY AT A DISTANCE WHICH PRODUCES THE DESIREDCHARACTERISTIC IMPEDANCE AND LEADING TO THE BALANCED LINE CONNECTIONASSEMBLY, AND (5) SAID INITIAL PORTIONS BEING DISPOSED IN MIRROR IMAGERELATIONSHIP WITH RESPECT TO SAID PLANE OF SYMMETRY WITH THE AXESTHEREOF DISPOSED WITHIN THE EQUIPOTENTIAL PLANE OF SAID LOOPS.